Development of a multiplex RT-PCR method for the detection of four porcine enteric coronaviruses

Effective preparation and immunogenicity analysis of antigenic proteins for prevention of porcine enteropathogenic coronaviruses PEDV/TGEV/PDCoV

Porcine epidemic diarrhea virus (PEDV), transmissible gastroenteritis virus (TGEV) and porcine deltacoronavirus (PDCoV) cause highly contagious gastrointestinal damage to piglets with high coinfection in clinical. However, there is no available trivalent vaccine against the three viruses. Here, a trivalent subunit vaccine by combining PEDV-SCOE, TGEV-SAD, and PDCoV-RBD proteins with ISA 201 adjuvant was effectively prepared, and the immunogenicity was evaluated. The detection results showed that the vaccine induced specific humoral IgG, neutralizing antibodies, and increased levels of Th1 and Th2 cytokines. Splenocytes proliferation and specific cytotoxic T lymphocytes (CTL) were activated. Furthermore, the three antigenic proteins up-regulated CD4+ and CD8+ T lymphocytes, activated the germinal center (GC) through the Tfh-GC axis, and promoted the differentiation of GC B cells in to plasma cells and memory B cells. Overall, the three antigenic proteins will provide helpful information for further exploration of trivalent vaccines against PEDV, TGEV, and PDCoV.

Advances in porcine epidemic diarrhea virus research: genome, epidemiology, vaccines, and detection methods

Porcine epidemic diarrhea (PED) is a highly contagious intestinal disease caused by the porcine epidemic diarrhea virus (PEDV). The economic impact of PEDV on the global pig industry has been significant, resulting in considerable losses. This paper presents a review of the latest research progress on PEDV genome, molecular epidemiology, vaccine development, and molecular detection methods. It was determined that the genetic diversity of the PEDV spike (S) gene was closely associated with the epidemiological trend of PEDV. The prevalence of S gene variants of different genotypes exhibited variability across regions and pig populations. Epidemiological analyses have demonstrated that PEDV can be transmitted via multiple routes, including direct contact, airborne aerosol, and water source contamination. With regard to vaccine research, the available vaccines can be classified into several categories, including live-attenuated vaccines, inactivated vaccines, subunit vaccines, bacterial vector vaccines, viral vector vaccines, mRNA vaccines, etc. Each of these has distinctive characteristics in terms of immunogenicity, protection efficiency, and safety. Molecular detection methods, including PCR-based methods, isothermal amplification techniques, immunological assays, and biosensors, play an important role in the diagnosis and monitoring of PEDV. Furthermore, this paper examines the current developments in PEDV research and identifies the key areas of future investigation. The objective of this paper is to establish a theoretical foundation for the prevention and control strategies of PED, and to provide a point of reference for further research on the genomics, epidemiology, vaccine development and detection methods of PEDV.

Establishment of a novel double-antibody sandwich fluorescence microsphere immunochromatographic test strip for rapid detection of swine acute diarrhea syndrome coronavirus (SADS-CoV) infection

Introduction

Swine acute diarrhea syndrome coronavirus (SADS-CoV) is an enveloped, positive-sense, single-stranded RNA virus that causes clinical symptoms such as vomiting and diarrhea in 10-day-old piglets. SADS-CoV has caused significant economic losses in the swine industry in southern China. Currently, no effective treatments or vaccines are available for this disease, making it crucial to establish a point-of-care testing (POCT) technology for early diagnosis and prevention.

Methods

In this study, we first validated the specificity and immunogenicity of four monoclonal antibodies (mAbs) targeting the nucleocapsid (N) protein of swine acute diarrhea syndrome coronavirus (SADS-CoV). The optimal antibody pair for constructing the fluorescent microsphere-based immunochromatographic assay (FM-ICA) was determined through systematic pairwise screening. Critical parameters of the FM-ICA test strip, including antibody labeling concentration, coating concentration, incubation time, and sample dilution ratio, were subsequently optimized. Analytical performance characteristics of the developed FM-ICA were then rigorously evaluated. Finally, clinical validation was conducted by parallel testing of 72 field samples using both FM-ICA and quantitative PCR (qPCR), followed by concordance rate analysis.

Results

First, we demonstrated that all four monoclonal antibodies exhibited favorable immunogenicity and specificity. Subsequently, mAb 12E1 was identified as the coating antibody, and mAb 5G12 was selected as the labeled antibody, forming the optimal combination for FM-ICA preparation. After optimization, the ideal parameters were determined: a labeling concentration of 200 μg/mg for antibodies, a coating concentration of 1 mg/mL, an incubation time of 10 min, and a dilution factor of 10. The FM-ICA exhibited outstanding specificity, sensitivity, reproducibility, and stability, achieving a maximum detectable dilution factor of 1280 and a limit of detection (LOD) of 78 PFU mL⁻¹. Finally, the concordance rate between FM-ICA and qPCR for clinical samples reached 97.22%.

Discussion

These results indicate that FM-ICA is an excellent POCT technology that can be used for the early diagnosis of SADS-CoV, providing support for disease prevention and treatment.

Evolution and virulence of porcine epidemic diarrhea virus following in vitro and in vivo propagation

Practice of inoculating porcine epidemic diarrhea virus (PEDV) in piglets generating feedback material might influence the genetic evolution and attenuation of PEDV. The study was conducted to evaluate evolutionary rate and attenuation following serial in vitro and in vivo propagation. In the study, PED-JPFP0-PJ, Passage 0 (P0), was isolated from infected pigs and serially passaged in Vero cells for 5 consecutive times, P1-P5. P0, P2 and P5 were then subjected to orally inoculate 3-day-old piglets. At 24 h post inoculation, intestines of each passage (F1), were collected, and subsequently sub-passaged in piglets for 2 additional passages (F2-F3). Virus titration, PEDV genomic copies number, VH:CD ratios, and immunohistochemistry were evaluated. S and ORF3 genes were characterized. The results of the study demonstrated that virus titer and virulence were negatively correlated with increased passages, both in vitro and in vivo. Increased substitution rate was observed in higher passages. The evolutionary rate of S gene was higher than that of ORF3. Seven aa changes at positions 223, 291, 317, 607, 694, 1114 and 1199, with reduced N-linked glycan were observed in P5F3. In conclusion, serial passage of PEDV, both in vitro and in vivo, influence the genetic development and the attenuation of PEDV.

Development of a multiplex reverse transcription-quantitative PCR (qPCR) method for detecting common causative agents of swine viral diarrhea in China

BACKGROUND

Diarrheal diseases caused by viral agents have led to a great morbidity, mortality, and economic loss in global pig industry. Porcine epidemic diarrhea virus (PEDV), transmissible gastroenteritis virus (TGEV), porcine deltacoronavirus (PDCoV), and group A porcine rotavirus (RVA) are main causative agents of swine viral diarrhea with similar clinical signs on Chinese farms and their co-infection is also common. However, it is still lack of a convenient method to detect these four agents.

METHODS

A TaqMan multiplex qPCR method was developed to detect PEDV, TGEV, PDCoV, and RVA, simultaneously. This method was then applied to investigate 7,342 swine fecal samples or rectal swabs, as well as 1,246 swine intestinal samples collected from 2075 farms in China in 2022.

RESULTS

Minimum detection limits of this method were 3 copies/µL for PEDV, 4 copies/µL for TGEV, 8 copies/µL for RVA, and 8 copies/µL for PDCoV, suggesting a good sensitivity. No signals were observed by using this method detecting other viral agents commonly prevalent in pigs, which is suggestive of a good specificity. Application of this method on investigating clinical samples demonstrated a relatively high positive rate for PEDV (22.21%, 1907/8588) and RVA (44.00%, 3779/8588). In addition, co-infection between PEDV and RVA was observed on 360 investigated farms, accounting for 17.35% (360/2075) of the farms where co-infection events were screened.

CONCLUSIONS

A TaqMan multiplex qPCR method targeting PEDV, TGEV, PDCoV, and RVA was developed in this study. This method demonstrated a good specificity and sensitivity on investigating these four common viruses responsible for viral diarrhea on Chinese pig farms, which represents a convenient method for the monitoring and differential diagnosis of swine viral diarrhea.

Triplex-Loop-Mediated Isothermal Amplification Combined with a Lateral Flow Immunoassay for the Simultaneous Detection of Three Pathogens of Porcine Viral Diarrhea Syndrome in Swine

Porcine epidemic diarrhea virus (PEDV), porcine bocavirus (PBoV), and porcine rotavirus (PoRV) are associated with porcine viral diarrhea. In this study, triplex loop-mediated isothermal amplification (LAMP) combined with a lateral flow dipstick (LFD) was established for the simultaneous detection of PEDV, PoRV, and PBoV. The PEDV-gp6, PoRV-vp6, and PBoV-vp1 genes were selected to design LAMP primers. The amplification could be carried out at 64 °C using a miniature metal bath within 30 min. The triplex LAMP-LFD assay exhibited no cross-reactions with other porcine pathogens. The limits of detection (LODs) of PEDV, PoRV, and PBoV were 2.40 × 10¹ copies/μL, 2.89 × 10¹ copies/μL, and 2.52 × 10¹ copies/μL, respectively. The consistency between rt-qPCR and the triplex LAMP-LFD was over 99% in field samples testing. In general, the triplex LAMP-LFD assay was suitable for the rapid and simultaneous detection of the three viruses in the field.